1. Field of the Invention
This invention relates to a liquid jet recording head and a recording apparatus by use thereof, particularly to a liquid jet recording head to be used for the liquid jet recording system which performs recording by discharging liquid for recording such as ink, and the like to attach it onto a recording medium such as paper, and a recording apparatus by use thereof.
2. Related Background Art
The liquid jet recording system which performs recording by discharging liquid for recording such as ink and the like to attach it onto a recording medium such as paper is extremely small to negligible extent in generation of noise during recording, and also enables high speed recording. Yet, it is attracting attention as the recording system capable of performing recording on a plain paper without requiring a special treatment such as fixing, and various types have been recently actively studied.
The recording head of the recording apparatus to be used in the liquid jet recording system is generally constituted by having an orifice (discharge opening) for discharging liquid for recording, a liquid path communicated with the orifice and having a portion at which the energy for discharging liquid for recording acts on the liquid for recording, and a liquid chamber for storing the liquid for recording to be supplied to the liquid path.
The energy for discharging the liquid for recording during recording is mostly generated by a discharge energy generating element of various types such as heat-generating element, a piezoelectric element arranged at a predetermined position of the portion (energy acting portion) where the discharge energy is acted on the liquid for recording constituting a part of the liquid path.
As the method for preparing a liquid jet recording head of such constitution, there may be included, for example, the method including the steps of forming a fine groove on a flat plate such as of glass, metal, and the like by cutting, etching, and the like and further forming a liquid path by bonding another appropriate plate to the flat plate having such groove formed thereon to form a liquid path, or the method including the steps of forming a wall of a photosensitive resin cured on a substrate having, for example, a discharge energy generating element arranged thereon by photolithographic step to provide a groove which becomes the liquid path on the substrate and bonding another flat plate (cover) to the grooved plate thus formed to form a liquid path (for example, U.S. Pat. No. 4,417,251).
Among these methods for preparation of liquid jet recording head, the latter method of employing a photosensitive resin can finely work the liquid path with better precision, and with better yield, as compared with the former method, and also bulk production can be realized more easily, and therefore it has the advantage that a liquid jet recording head with better quality and lower cost can be provided.
As the photosensitive resin for preparation of such a recording head, there have been used those which have been used for pattern formation in printing plate, print wiring, and the like, those known as the coating material or adhesive of the photocurable type to be used for glass, metal, ceramics, etc., and also primarily resins of the dry film type from the aspect of working efficiency.
In the recording head utilizing a cured film of a photosensitive resin for a part of the constitution, for obtaining excellent characteristics such as high degree of recording characteristic, durability and reliability, and the like, the photosensitive resin to be used is required to have such characteristics as:
(1) particularly excellent adhesion to the substrate, etc. as the cured film;
(2) excellent mechanical strength and durability when cured;
(3) excellent sensitivity and resolution during patterning by use of pattern exposure.
Whereas, few of the known photosensitive resins which have been employed for formation of liquid jet recording heads up to date fully satisfied all of the characteristics as mentioned above under the present situation.
As the photosensitive resin for recording heads, for example, those employed for pattern formation in printing plate, print wiring, etc., although excellent in sensitivity and resolution, are not satisfactory in such demands as adhesion and close contact with glass, ceramics, plastic films, etc. used as a substrate in most cases, and also sometimes insufficient in mechanical strength or durability when cured. For this reason, in the step of preparing a recording head or as accompanied with use of a recording head, there may sometimes ensue such problem that deformation, peel-off from the substrate, damage of the resin cured film which may be a cause for remarkable damage of the reliability of the recording head such as lowering in recording characteristics by inteference of the flow of the liquid for recording within the liquid path, or making the liquid discharge direction unstable.
On the other hand, those known as the photocurable type coating material or adhesive to be used for glass, metal, ceramics, etc., although having such advantages that they are excellent in close contact or adhesion with the substrates comprising these materials, and also that sufficient mechanical strength and durability are obtained when cured, are not satisfactory in the demands of sensitivity and resolution in most cases, whereby an exposure device of higher intensity or prolonged exposure operation are required. Also, in their characteristics, no highly precise high density pattern can be hardly obtained with good resolution, and therefore such resins have the problem that they are not suitable for recording heads for which fine precise working is particularly required.
Also, in the photosensitive resin compositions utilized for various uses of the prior art, adhesion with metal, etc. has been improved by addition of various additives such as heterocyclic compounds having complex forming ability with metals, etc., or coupling agents, etc. into the photosensitive resin composition (Japanese Patent Publication Nos. 51-5934, 58-24035, etc.). However, this method had the problem that the above additive aids, etc. caused such phenomena as oxidation and corrosion of the composition, etc. after elapse of a long term.
On the other hand, for the purpose of obtaining a cured composition having sufficient adhesion without addition of such additive aids, a polymeric substance comprising a graft copolymer having polar group in the branched chains is disclosed in Japanese Laid-open Patent Application Nos. 61-283645, 61-283646. The active energy-ray-curing resin composition containing the polymeric substance (graft copolymerized polymer) disclosed in the applications has the advantage that improvement of adhesion, further improvement of durability of the coating can be realized without relying on additive aids, etc.
However, in this composition, there still remained the problem that difficulty is accompanied with the molecular design of the polymeric substance (graft copolymerized polymer). More specifically, there is generally accompanied technical difficulty in synthesizing a graft copolymer so that its whole weight average molecular weight may become a suitable desired molecular weight over a wide range (about 50,000 to 350,000) while maintaining the molecular weight of the graft chain and its content at constant levels.
Shortly speaking, for making good the developing characteristics during pattern formation, namely dissolving rate of the unpolymerized portion, swellability of the polymerized portion, and sensitivity, sharpness of pattern, resolution as the results of them, the average molecular weight of the polymeric substance must not be too small. In the graft copolymerized polymer, it is accompanied with difficulty from the point of steric hindrance in the synthetic technique at the present time to obtain an average molecular weight in conformity with the above-mentioned object by bonding a large number of graft chains having enough lengths to obtain effective adhesion to the trunk chain of a relatively larger molecular weight.
In other words, if the average molecular weight of the polymeric substance is too low, the developing characteristics of the pattern forming material by use thereof, namely dissolving Pate of the unpolymerized portion, swellability of the polymerized portion, and sensitivity, sharpness of pattern, control of resolution are limited to some extent.
Thus, the photosensitive resin composition to be used as the constituent material of a liquid jet recording head (ink jet recording head) is required to have characteristics of extremely high performance.
Specifically, the characteristics demanded for the photosensitive resin composition may be mentioned as follows:
(1) The composition should be such that when formed into a cured film, the film is completely or substantially free from dissolution into ink, and should not cause problems such as generation of a foreign matter which may cause clogging of discharge opening or liquid path or change in discharge characteristics by change in ink properties;
(2) The composition should be such that when formed into a cured film, the film causes no lowering in strength or change in dimensions as the structural material such as swelling, peel-off, generation of cracks by penetration of ink;
(3) The composition should be such that when applied as a cured film to a recording head in which particularly, heat energy is utilized as the liquid discharging energy, there occurs no deformation of the shape, etc. by the pressure for liquid discharging and the thermal shock and the like.
This is because the photosensitive resin composition (or its cured product) is constantly in contact with ink (water-soluble organic solvents of high polarity are used therein in most cases), whereby the problem will readily occur that residual soluble components are dissolved into ink.
Also, lowering in strength, change in dimensions as the structural material, in addition to giving great restrictions in design of ink, add great restrictions in durability, design of the recording head itself.
Further, due to the synergetic action of heat and pressure, there may be sometimes generated such problems as deformation, etching, etc. as the structural material.